Paramount Parks owns Kings Island in Ohio (as seen on The Brady Bunch), Kings Dominion in Virginia, Carowinds on the North/South Carolina border, Great America in the Bay Area, and Canada's Wonderland in Toronto.
Cedar Fair started out as an unholy alliance between Cedar Point in Ohio and Valleyfair! in Minnesota. Well, ok, maybe it wasn't unholy, but it's always fun to say "unholy alliance." Later on, Cedar Fair acquired Knott's Berry Farm, Dorney Park in Allentown PA, Worlds of Fun in Kansas City, Michigan's Adventure in Alabama (no, Michigan, what do you think?!) and, recently purchased from Six Flags, good ol' Geauga Lake near Cleveland.
That means there's now four major amusement chains in the US: Disney, Six Flags, Cedar Fair, and bringing up the rear, Busch Gardens. (Kennywood's got holdings but, let's face it, it's not a major player.) Not only that, but Cedar Fair now owns the three major parks in Ohio. Things just got a lot more interesting.